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The
Energy-Water Collision
Water and energy are intertwined. Producing energy uses water,
and providing freshwater uses energy. Both these processes face
growing limits and problems.
In most power plants, water cools the steam that spins the
electricity-generating turbines. Refining transportation fuels
requires water, as does producing fuels-for example, mining coal,
extracting petroleum, or growing crops for biofuels. Using water in
our homes and businesses requires energy to get it there, treat it,
heat it, and more.
Because of these links between energy and water, problems for
one can create problems for the other. In places where using energy
requires a large share of available water, or where water resources
are scarce or stressed by competing pressures (such as the needs of
farmers or of local ecosystems or, increasingly in many parts of the
United States, by climate change), the energy-water connection can
turn into a collision-with dangerous implications for both.
A number of technologies offer strong opportunities to address
the water-related impacts of our energy use. One of the easiest
solutions is also the most cost-effective: using less electricity or
transportation fuel by making appliances, buildings, and vehicles
more efficient.
Using renewable energy technologies such as wind and
photovoltaics means doing away entirely with water use for
electricity production. Given the many connections between energy and
water, the choices we make in the near future about how we produce
and use energy will determine how resilient our energy system is to
the variability of our water resources and the many competing demands
for it. www.ucsusa.org/clean_energy/technology_and_impacts/impacts
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Getting
to Net-zero
Design and
other considerations for a net-zero home
by Jennifer Barker
The home at the John Day Fossil Beds National Monument that we
reviewed in our fall issue of Energy Independence Sol-utions was
designed to be a "net-zero" home. The phrase
"net-zero" is tossed around a lot these days, but what
exactly does it mean?
When it refers to a home or commercial building,
"net-zero" means that the amount of renewable energy
produced on-site is equal to or greater than the amount consumed by
the site. Production and consumption are usually annualized to
average out seasonal variations. Unless the issue is specifically
addressed, it does not include the amount of energy consumed by the
site's occupants for transportation, food or goods brought to the
site, or off-site activities.
How were the systems at the home in the Fossil Beds NM
designed to be "net-zero," and how is it actually
performing? To find out, we checked in with solar designer and
installer Dean Abney, of Abney Solar Electrix. |
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You must use easily available, less
expensive and lower-tech methods to reduce energy consumption first,
before you try to produce all of a home's energy with solar or other renewables.
It does not matter how much money you have, no amount of
renewables can turn an inefficient house into a net-zero home.
Utilizing strategies like building orientation/placement/ color;
window size/glass/daylighting/shading, passive solar, and solar hot
water can significantly lower the need for energy inputs with less
up-front investment. Some of these strategies cost absolutely nothing
("free lunch"), but give you positive returns for merely
investing some thought into your design. All these strategies put
together will make the solar electrician's job easier and less expensive.
Designing the energy systems to work
together is a big part of the picture.
The home was designed by the architect to be passive solar
heated. Supplemental heat, if needed is provided by a
high-efficiency, ductless split-unit heat pump (which was not needed
at all until November). The home is all-electric, with appliances and
lighting specially chosen for energy efficiency. The Park Service
wanted to produce enough extra energy in summer to run a daily charge
on their Polaris electric 4x4 vehicle.
Abney consulted with the architect over the load calculations,
and made suggestions based on experience for modifying the load
estimates or system sizing. When everyone was happy with the load
calculations, he designed a system that included a 2820 Watt solar
array, a SunnyBoy 6000US Inverter, and a Midnite MNPV Combiner Box
(on a roof that was designed to pitch the solar array perfectly for
maximum production at the latitude).
Solar hot water also plays a part in the renewable energy
setup at the Fossil Beds home. Mike Hewitt of E2 Solar Energy
installed the two-panel solar hot water system. It was sized to
maximize hot water production, so that no electric water heating
would be needed except in mid-winter months. A drainback feature
mitigates any overheating issues.
The home was designed to have a HERS
rating of -15. A standard American home has a rating of 100, and a
Zero-net home has a rating of zero. So what does a negative rating mean?
A negative HERS (Home Energy Rating System) rating means that
the home produces more energy than it uses. So far the house at the
Fossil Beds has produced enough surplus over the last ten months to
power a Mitsubishi i-MIEV (4-passenger electric vehicle) for about
18,740 miles.
You can design a home to be net-zero, but
that doesn't necessarily mean that it will be a net-zero home for the
people living in it.
Eight nearly identical high-performance single family homes in
Massachusetts produced equal amounts of solar PV electricity, yet two
of the homes used ten percent less electricity than they produced,
and others used up to 72 percent more electricity than produced by
their arrays. Why was this?
To be net-zero, you have to live net-zero. Study authors found
that the Massachusetts homos' performance ultimately came down to
household size and behavior. As energy consultant Andy Shapiro says,
"There are no zero-energy houses, only zero-energy
families." Lighting/ appliances and hot water use made up almost
all of the differences in total energy consumed.
Can these methods be used to turn an
existing home into a net-zero home?
Any home's energy balance can be improved by investing time,
thought, and money into the project. Whether you make it all the way
to net-zero or not, any improvement at all is a benefit to your long
term cash-flow. Compare the returns with those you can get for other
investments these days, and you'll find energy reduction strategies
will pay good dividends in the form of both cash saved, and comforts enjoyed! |
